A superconducting wire is manufactured by superposing a metal substrate, an intermediate layer composed of one or more layers of oxides, such as cerium oxide (CeO2), yttria-stabilized zirconia (YSZ), and yttrium oxide (Y2O3), and a superconducting layer (RE123 film, RE: Y, Gd, Ho, or the like) on top of each other.
Methods known as techniques for manufacturing crystal-oriented superconducting layers are: the ion-beam-assisted deposition method (IBAD method) that involves depositing a textured intermediate layer on a non-textured metal substrate such as hastelloy, so as to allow the superconducting layer to take on the texture; and a method that involves the use of a biaxially textured metal substrate, so as to allow the intermediate layer and the superconducting layer to take on the texture (e.g., a method involving the use of a rolling-assisted biaxially textured substrate (RABiTS)). The latter method is more advantageous than the former in view of factors concerning future production efficiency, such as film deposition rate. In order to improve superconductivity, a metal substrate is required to have a high degree of biaxial crystal orientation. The crystal orientation of a metal substrate is evaluated in terms of, for example, the c-axis orientation rate, the Δω value (an out-of-plane orientation index), and the Δϕ value (an in-plane orientation index) of the outermost layer of the substrate.
A substrate known as such a metal substrate (a substrate for a superconducting wire) is produced by superposing crystal-oriented copper on a stainless substrate and further superposing nickel thereon. For example, Patent Document 1 discloses an orientation substrate for the epitaxial film formation in which a metal substrate as a reinforcing material is claded to an orientation metal layer consisting of oriented copper, the orientation metal layer is a metal having an orientation in which both orientation degrees Δϕ and Δω are 5 to 9 degrees, an orientation improvement layer of a thickness of 100-5,000 nm consisting of a nickel plating film is provided on a surface of the orientation metal layer, and the differences between the orientation degrees (Δϕ and Δω) on the orientation metal layer surface and the orientation degrees (Δϕ and Δω) on the orientation improvement layer surface are 0.1 to 3.0 degrees.